The present invention relates to fabricating waveguide materials for the fiber-based materials industry and, more particularly, to a novel ampoule that provides for a contaminant-free, chalcogenide glass tubing fabrication process.
In the fabrication of waveguiding fibers for tele-communications, chalcogenide glasses (non-oxide glasses, based on sulfur, selenium and tellurium) are candidate materials for providing low loss transmission in the near to mid infrared. Moreover, rare-earth doped chalcogenide glasses are useful materials for the fabrication of efficient optical amplifiers and/or lasers. In particular, Pr-doped, (GeAs) sulfide glasses are considered promising materials for providing gain in the range of 1,300 nm, as taught by B. G. Aitken et al. in U.S. Pat. No. 5,389,584 for Ga- AND/OR In- CONTAINING AsGe SULFIDE GLASSES. At present, the best fiber design consists of a Pr-doped, Ga-codoped, GeAs sulfide core that is surrounded by a lower index GePAs or GeAs sulfide cladding, as taught by B. G. Aitken et al. in copending patent application, Serial No. 09/530,831, filed on May 3, 2000, and hereby incorporated by reference.
In order to fabricate rod-in-tube preforms of this material or other chalcogenide glasses that can be redrawn into fibers, a necessary first step requires making tubing from the selected cladding glass. The current method used to produce such tubing consists of a two step process. First, the batch material is loaded into a melting ampoule, and then melted and quenched to form a solid cylindrical glass rod. Then, the glass rod is loaded into a forming ampoule, melted, spun cast upon a mechanical lathe and quenched into glass tubing.
The solid glass rod can become contaminated during its removal from the xe2x80x9cmeltingxe2x80x9d ampoule, and also while transferring and loading it into the xe2x80x9cformingxe2x80x9d ampoule. For example, the surface of the pristine, solid glass rod can be contaminated with air-borne particles, silica pieces from the fractured xe2x80x9cmeltingxe2x80x9d ampoule, and other impurities. These adulterants can cause partial devitrification of the cladding glass during preform redraw, which results in fiber attenuation losses that are much greater than the theoretical minimum.
As a practical matter, a 1,300 nm amplifier fiber must have an attenuation loss no greater than 1 dB/m. Other applications, such as sensing or laser-power delivery, require even lower loss. Therefore, it would be immensely beneficial to eliminate any chance of introducing potential impurities during the chalcogenide fiber fabrication process.
The present invention reflects the discovery that spun-cast tubing of chalcogenide glass to be used as cladding or fiber can be fabricated directly from batch materials in a single apparatus process. The new, single apparatus process eliminates the transferring step.
The current invention provides a novel ampoule design that combines the melting and spinning steps within the ampoule, and hence prevents introduction of impurities.
In accordance with the present invention, there is provided an apparatus and method for fabricating chalcogenide glass tubing to be used in making fibers. The apparatus comprises a new melt/spin ampoule for melting and forming chalcogenide glass materials. The ampoule comprises three sections. The first section comprises a loading chamber that is open at one end and attached to a second chamber at its other end. The loading chamber is provided with a small external flange, whose orientation is coplanar with a bent drainage tube that is disposed in the second melting This second section is attached to, but separated from the third section (a forming or spin casting channel) by a septum that is fitted with the drainage tube. The drainage tube is centered in the septum and extends into the melting chamber. The tube is bent in an arc that terminates close to the side wall of the melting chamber.
The requisite raw materials for making the chalcogenide tubing, including but not limited to elemental Ge, As, P and S, are introduced into the open end of the first ampoule section. The loaded ampoule is evacuated and then sealed by heating the wall of the first section to collapse the tubing. The sealed ampoule is then placed in a rocking furnace in such a way that the external flange on the loading chamber and, hence, the open end of the drainage tube is located in an upright position. This procedure ensures that, at high temperature, and with the rocking motion (approximately xc2x130xc2x0 from horizontal) of the furnace, molten glass is prevented from flowing into the forming chamber.
The ampoule is then heated to produce a homogeneous chalcogenide melt in the melting chamber. The heated ampoule containing the chalcogenide melt is then transferred to a vertical furnace operating at approximately the final melting temperature. The ampoule is suspended with an orientation that allows the chalcogenide melt to drain into the forming chamber.
The hot ampoule is then removed from the furnace, attached to a lathe, and spun in order to form the chalcogenide glass tubing. The ampoule is then removed from the lathe and quenched. This causes the chalcogenide glass tubing to delaminate from the ampoule wall, and prevents cracking as the ampoule cools to ambient temperature.